"NASA’s Curiosity rover usually keeps its instruments firmly focused on Mars’s ground, zapping grit with its laser or drilling cores in bedrock."

'Well into its fifth year, the rover has now shot more than 500 movies of the clouds above it, including the first ground-based view of martian clouds shaped by gravity waves, researchers reported here this week at the Lunar and Planetary Science Conference. (Gravity waves, common atmospheric ripples on Earth that result from air trying to regain its vertical balance, should not be confused with gravitational waves, cosmological ripples in spacetime.) The shots are the best record made so far of a mysterious recurring belt of equatorial clouds known to influence the martian climate.

'Understanding these clouds will help inform estimates of ground ice depth and perhaps recurring slope lineae, potential flows of salty water on the surface, says John Moores, a planetary scientist at York University in Toronto, Canada, who led the study with his graduate student, Jake Kloos. “If we wish to understand the water story of Mars’s past,” Moores says, “we first need to [separate out] contributions from the present-day water cycle.”'